Video: Top-Grafting Cucumbers Demonstration | Johnny's Selected Seeds

Two reliable, straightforward techniques for top-grafting greenhouse cucumber variety scions onto squash rootstock

Here we are in Johnny's seeding house, which is an area that we typically use to germinate our seeds for the trial season. We keep it at about 85°F (~30°C) and at high relative humidity, so it's a good place as well to do grafting.

Now I'd like to take you through some of the techniques of cucurbit grafting:

  • 2 different methods of top-grafting cucumbers;
  • PLUS tricks and issues that I've come across in the years I've done it here at Johnny's.

Here is the setup that I have for starting my grafting. Here are a few plants that I've already grafted using the first technique that I'll be showing you. I find it helpful to have everything on hand, as well as having a clean workspace that I can use.

The scions here were [seeded] about 3 days ahead of the rootstock. The rootstock has gotten slightly bigger than is ideal, just given the nature of things here. It's January, so everything is being done inside, under lights, and it can be quick for things to get a little bit leggy. Fortunately, there is a technique that you can use, and that I'll be talking about, to help when the rootstocks have gotten a bit leggy. So, in a way, this is a good example.

Starting with this rootstock, you have the two cotyledons and the first true leaf, which has just started to expand, as well as the growing point, and this is a good stage to be grafting, because the plants have developed enough that they can handle the stresses of being grafted, but there isn't so much tissue that they will collapse, once you've basically cut a big hole in them.

So, unlike with tomato grafting, when you're top-grafting cucumbers, you actually want to leave one of the cotyledons. And I typically cut down at about a 45° angle, removing all the meristematic tissue, just starting to see that you're cutting into the stem, but without completely hollowing it out, and leaving one cotyledon. It's important to remove all of the meristematic tissue, or else you can have the rootstock start to regrow. But, it's also important not to cut too deep, in which case the rootstock will often collapse under the scion, and the graft won't take.

I think all I can really say to that is, "Practice makes perfect," and don't be afraid to seed a few extra rootstock ahead of time, so that you can really get a feel for the technique before it counts.

In cutting the scion, I find, with the square stems of cucumbers, I usually like to go on a flat side down at about a 45° angle, and that way, when I attach it to the rootstock, the angles are much flatter, and you'll have less chance of space developing as it heals.

In attaching the scion, it's important to find ones where the diameter of the stem of the scion and the diameter of the stem of the rootstock are as similar as possible, which can be challenging, given that the rootstock is a squash and, obviously, the scion is cucumber. Fortunately, by offsetting the timing it's a little bit easier for you to find comparable stem diameters. And one of the nice things about cucumber grafting is that it's actually a little bit more forgiving than tomato grafting, and if the size isn't exactly the same, the graft can still heal fairly nicely.

So you want to attach the scion to the rootstock with good contact, making sure the cut ends are overlapping, inserting the clip like so, so that they are firmly joined together before inserting the support.

The second technique is going to feel very counterintuitive to a lot of people. I was definitely pretty surprised by it, when it was taught to me, but it offers a number of advantages over top-grafting the plant in the tray itself. You start by cutting the roots off of the rootstock — which feels pretty insane — but I promise you that it will work out.

  • One of the benefits of this is that in this situation, where you have all of these very leggy rootstock plants, you can cut it to essentially the length that you want it.
  • In addition, rather than being hunched over a tray, trying to do all of the cuts and attachments with a plant that is attached by the roots to this tray, it's much easier to just have the rootstock in your hand, be able to manipulate it in space, and set it aside as you're going along.

Otherwise, the technique is very similar:

  • You're taking your razor blade...
  • You're cutting off one of the cotyledons, the true leaf, and that growing point...
  • You can just set that down here...
  • You're taking one of your scion plants, cutting it in the same way that we had discussed...
  • Picking the rootstock back up and attaching the scion to the rootstock, like so...
  • Putting the clip on...
  • Putting it into the soil...
  • And inserting your support.

I would say, if you're in an environment that has high humidity and a warmer temperature, like in here, you can actually do a few of these at a time. You don't want to get too far ahead of yourself, because as soon as you're cutting the roots and cutting the growing point off of things, they start to wilt. But for the sake of efficiency, I find that I can usually do about 5 in a batch, put them into the tray, mist them lightly — you don't want the plants to be overly wet but moist enough that they're not going to be respiring — and then move on to the next batch.

Once I have a tray completed, I typically cover it with one of these nice [Humidity Domes], and that way you can really ensure the humidity is kept as high as possible.

And then I have this healing chamber set up [inside this Grow Tent]. Starting out, everything is going to be in complete darkness. I want there to be as high humidity [as practicable], a temperature in the mid 80s°F (~30°C) or so. I have a humidifier set up in here, and then I have a grow light set up in here, so over time, as the healing chamber does its magic and the seedlings start to knit, you can put light in here, slowly increasing the amount of light, slowly decreasing the amount of humidity, until the plants are essentially at standard room conditions, at which point, ideally, the scar tissue is formed, you can take away the clips and the supports, and the plants will start growing together as one, ahead of transplanting.

So it is about a week and a half after the grafting was done, and the plants were put into this healing chamber, and overall, they've healed very nicely. You can see that they've started to put on new growth, which is a very good sign that your grafts have taken well and that the plants are through any sort of healing that they need. And in, probably, another week or so, they would be ready to transplant.

So they're still a little small to be pulling them out of their cells, like this, but I just wanted to show you how, despite cutting the roots off the rootstock, you can see they've started to develop new roots. I'm able to pull this whole plug out. It's still a little young to be doing that, but the healing has started.

Then here we have the area where the graft was made; you can see it was humid enough in there for there to be a few adventitious roots that have grown onto the scion itself. These aren't any particular big deal; once the plants are transplanted into a normal greenhouse without that level of humidity, I find that the adventitious roots just kind of air-prune out. You do need to make sure, when you're transplanting, that they aren't near the soil level itself, because if they are, they'll root into the ground, and then, if you have any soilborne diseases, they may go around the rootstock there. So, not that big a deal, but just something to be aware of.

But as you can see, the two plants have cleanly grafted there. And at this point the scion is able to take up water and nutrients through the rootstock, and relatively soon, we should be ready to transplant.

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